Unfire brick for melting steel electric furnace top BDL-80 BDL-75 AL2O3% ≥80 ≥75 Refractoriness ℃ ≥1780 ≥1780 initial softening point under load 0.2Mpa ℃ ≥1530 ≥1520 Apparent porosity % ≤18 ≤18 Cold compressive atrength MPa ≥≥60 ≥55 Castable material for ladle GBJ-1 GBJ-2 GBJ-3 AL2O3% ≥30 ≥70 ≥90 MgO% ≥60 ≥11 ≥7 Bulk density g/cm3 110℃?4h ≥2.9 ≥2.9 ≥3.0 1000℃?h ≥2.85 ≥2.80 ≥2.90 1550℃?h ≥2.8 ≥2.88 ≥2.95 cold compressive strength MPa 110℃?4h ≥45 ≥60 ≥45 1000℃?h ≥45 ≥50 ≥50 1550℃?h ≥40 ≥60 ≥70 MPa Modulus of repture 110℃?4h ≥6 ≥5 ≥7 1000℃?h ≥7 ≥8 ≥5 1550℃?h ≥8 ≥5 ≥8 Change of curve % 1000℃?h ≤0.5～1.2 ≤0.5～1.5 ≤0～0.8 1550℃?h ≤0～0.2 ≤0～0.2 ≤0～0.2 purpose Steel cover and bottom Middle and small size steel cover integer Middle and small size steel cover dreg line